The Cat Sìth (Scottish Gaelic: [k?aht? ??i?]) or Cat Sídhe (Irish: [kat?? ??i?]) is a fairy creature from Scottish mythology, said to resemble a large black cat with a white spot on its breast. Legend has it that the spectral cat haunts the Scottish Highlands. Some common folklore suggested that the Cat Sìth was not a fairy, but a transformed witch.

The myths surrounding this creature are more common in Scottish Folklore, but a few myths occur in Irish folklore as well.

The Cat Sidhe, in Faerie, has two forms: a stocky, powerful, bipedal fur-covered form with large teeth, claws, and tail; and a large stocky mountain cat type form. Cat Sidhe are skilled trackers, hunters, and guards who live in the Winter Court. Like most Fey in the Winter Court, they are more reserved than the Summer Court. Unlike most Fey, the Cat Sidhe are not immortal. They have long life spans, but they still age and die. Further, Ice Trolls (which do not live in Faerie) prize their pelts and hunt and kill them when they can.

When Cat Sidhe cross Iron Side, they are consigned to either a fully human looking form (bipedal, no fur, no fangs, no claws, no tail) or fully cat. They tend to prefer the cat form, as the human form leaves them feeling naked and defenseless. The longer they spend Iron Side, the more likely they are to be stuck in that form. As a human shaped Cat Sidhe cannot cross back into Faerie, this poses a problem.

Cat Sidhe do not tend to take part in political intrigue. Although intelligent, they are not devious or overly secretive (any more than any other feline influenced race).

Cat Sidhe, with their limited life span, do experience pregnancy– which is rare among Faerie. Females have 1-3 litters in their life time, of 3-7 kits. Generally, more males than females are born and survive. Cat Sidhe are able to interbreed with other fertile Fey creatures and humans, although it’s unlikely. Their offspring generally take after the non Cat Sidhe parent, although this is not always true, and are usually sterile.